Broad-band structured fluorescence from NaI

Abstract

The emission spectrum of a molecular beam of NaI has been measured following excitation by the 248 nm KrF line of an excimer laser. The fluorescence structure, and the lifetime (17±2 ns), indicate the presence of a bound upper state not previously characterized. We identify this state as correlating with Na(3 2P)+I(5 2P3/2) atoms. Through numerical simulation using a Morse function representation for the upper state, we have determined approximate values for the well depth of 530±260 cm−1, well breadth of ∼1.8 Å−1, and equilibrium separation of ∼3.4 Å for this state. As a consequence of the breadth of this weakly bound excited state the bound→bound line spectrum spans a broad spectral range (87% of the ground state well depth) entirely comparable with spectra attributed to free→bound emission.

Femtosecond Real-Time Probing of Reactions. 18. Experimental and Theoretical Mapping of Trajectories and Potentials in the NaI Dissociation Reaction

“…58 Figure 7 offers a diagrammatic comparison of the potential energy curve for the fluorescing state determined by FTS with those for the C 0 + state derived from spectroscopic studies in the frequency domain. 33,58 The value of D e ′′′ ) 1863 cm -1 reported here quantitatively accounts for the splitting times obtained at different probe wavelengths as a function of photolysis energy.…”

“…The intense fluorescence monitored by these authors was attributed to bound f bound and bound f free transitions of NaI, which swamped the weak free f bound emission from the [Na‚‚‚1] ‡ * transition states of reaction 1 observed by the same group in separate experiments at shorter photolysis wavelengths. 33,56,57 Bluhm et al have subsequently established the depth of the potential minimum of a state labeled C 0 + leading to the same covalent asymptote by laser excitation spectroscopy across the wavelength range 239 e λ e 256 nm. 43,58 Prior to these two studies, the existence of a state with a shallow potential energy well in the same energy range had only been tentatively inferred from absorption cross section measurements 29 and discussed in relation to an early fluorescence quenching study.…”

“…To demonstrate the robustness of the potentials derived in section III, we have carried out calculations using a Morse curve postulated for E 3 (R). 33 In this case, it was not possible to reproduce satisfactorily the experimental splitting data to quantitative accuracy: values of τ s ) 202 and 96 fs were calculated for λ 2 ) 600 and 640 nm, respectively, at λ 1 ) 320 nm, and τ s ) 225 and 102 fs for the same probe wavelengths at λ 1 ) 360 nm. The periods τ osc remain unchanged from before, of course, since the oscillation frequency depends only upon the λ 1 shape of E 2 (R).…”

A configuration interaction study of the ground and first excited 1∑+ states of the NaI molecule

“…Bluhm et al (5) and Bower et al (6) found a new bound state that leads to one of the Na(3p) asymptotes. Rose et al (7,8) performed femtosecond transition state spectra (FTS) measurements on the reaction of NaI, LiI, and NaBr.…”

Femtosecond Time-Resolved Pump−Probe Spectroscopy of NaI in Rare-Gas Environment

“…The C(0 + ) state can be described by a shallow Morse potential having a dissociation energy between about 500 and 2000 cm -1 . ,, As the probe pulse prepares the C(0 + ) state near its dissociation limit, vibrational relaxation due to collisions with rare-gas atoms might stabilize the NaI molecules below the dissociation limit. Again, argon atoms should result in a larger momentum transfer than helium atoms.…”